The present invention relates to control circuits for air conditioner compressor motors and other motors where it is very undesirable to reenergize a motor quickly after it has been deenergized. A principal use of such circuits is in connection with thermostatically controlled air conditioner units. In the absence of a delay circuit of the sort involved here, various circumstances could cause the air conditioner compressor motor to be energized soon after it was deenergized. One circumstance would be a manual or automatic adjustment of the thermostat to a lower temperature setting soon after it had turned the air conditioner off. Without an intervening delay device, there is a possibility that the air conditioner motor would be energized only a few seconds after it was deenergized. Although this possibility is not great, the deleterious effect should be avoided with virtual certainty.
In general, air conditioner timers for causing delay of reenergization of the compressor motor have been in widespread use for decades. Certain features of such devices make them more desirable; for example, it is convenient for a self-contained delay circuit to be installed by connecting only the two wires leading from the delay circuit in series with one side of a low voltage AC line from the thermostat to the air conditioner motor controller relay or similar device. In the past, most air conditioner timers required a source of power to operate the timer circuit other than the two wires which connected it in series in a line from the thermostat to the motor controller. Usually a third wire was provided which needed to be connected to the transformer or other low voltage source which provided current to the thermostat. Especially for replacement air conditioner delay timers, it is much more convenient if the repair or maintenance person can simply remove and/or shunt the old device and insert a new device by connecting its two wires into one side of the line from the thermostat to the air conditioner motor controller.
Another factor which influences the design of air conditioner delay timer devices is the undesirable effect of having to wait from one to five minutes for the air conditioner to start up on every occasion that the thermostat control produces a "make" or switch closed condition calling for air conditioning to be on. A delay timer which operates in this fashion is referred to as a delay-on-make timer. Other timers are available which commence a timing function when the break condition at the thermostat is detected, and, assuming there is not a too rapid reenergization by a "make" condition, the delay-on-break timer will time out, allowing reenergization of the air conditioner without delay. Still another factor is involved in that while the delay-on-break timer function is preferred for usual on-off operations, it is not desirable in the case of a general power failure. The reason for this is that one wishes to take advantage of the random differences in the delay time for a large number of air conditioners on one main power circuit as in a hotel or motel. The varied delays prevent the air conditioners all from turning on at once when the power is restored; if all or most of the air conditioners lad delay-on-break timers and the power outage was sufficiently long then all air conditioners would turn on instantaneously when the power was restored, in most cases causing overload of a main circuit breaker. In a motel, for example, this would require most of the air conditioners to be physically turned off before the circuit breaker could be reset without being tripped by excessive current demand. It will therefore be seen that it is desirable, if not essential, that air conditioner delay timers have a delay-on-make operation whenever there has been a power failure.
In contrast to prior devices available, the present two-wire air conditioner timer with delay-on-break feature deals with each of these factors in a highly satisfactory manner, avoiding all of the difficulties mentioned above.